<!DOCTYPE html>
<meta charset="utf-8">
<title>Page with third-party iframe</title>
<body>
<script>
function addIframe(url) {
  return new Promise(resolve => {
    const iframe = document.createElement('iframe');
    iframe.src = url;
    iframe.onload = () => {resolve(true);};
    document.body.appendChild(iframe);
  });
}
</script>
</body>
